1. Field of the Invention
The present invention is directed generally to an apparatus and method for reactive ion etching wherein a high frequency plasma is generated between two electrodes, one of which carries a substrate to be etched.
2. Description of the Related Art
In a known apparatus for reactive ion etching, having a pair of electrodes between which is generated a high frequency plasma, a low frequency voltage having a sinusoidal waveform is applied by capacitive coupling to the electrode on which the substrate to be etched is arranged. A negative half-wave portion of the sinusoidal waveform acts as an extraction voltage for the ions. The sinusoidal waveform is applied as the extraction voltage because a generally insulating substrate electrically charges according to an exponential function due to the ion bombardment if an extraction voltage in the form of a negative DC voltage is applied to the second electrode. The electrical charging of the substrate reduces the ion energy and etching comes to a standstill.
By applying a low frequency, sinusoidal voltage having a negative half-wave to the second electrode, the electrical charging of the substrate effected by ion bombardment which is due to electron bombardment during the positive half-wave of the voltage is avoided. A moderate equilibrium potential, or voltage, is formed at the substrate on which, however, the low frequency voltage continues to be superimposed. The ion energy is thus not constant.